Pregnancy and Birth Flashcards
fertilization
the union of a sperm with an egg to form a zygote
fertilization typically occurs in
the ampulla of a Fallopian tube
semen is deposited into the vagina as a liquid, but
fibrinogenase converts fibrinogen into a fibrin clot within one minute to prevent semen from leaking out of the vagina, and also to protect the sperm from the acidity of the vagina
after about 20 minutes,
vaginal acidity in neutralized and sperm can survive so semen clot liquefies
of the several hundred million sperm ejaculated into vagina,
fewer than 1% survive
the cervix contains a maze of
folds and outpocketings that can easily trap sperm
shortly before ovulation,
cervical mucus becomes thinner to facilitate passage of sperm through cervix
approx one million sperm survive
journey through cervix
the uterine cavity is filled with
a watery fluid through which sperm can easily pass
only a few thousand sperm survive to enter the Fallopian tubes and
they move through the Fallopian tubes assisted by ciliary action
only 50 to 100 sperm will actually reach
a secondary oocyte
sperm appear to be drawn toward
an oocyte by some type of chemical communication, but before they can fertilize an oocyte they must undergo capacitation
capacitation probably removes
a protective coating from head of a sperm that blocks release of acrosome enzymes needed for penetration of secondary oocyte
when sperm approach a secondary oocyte,
small openings form in the acrosome which allows enzymes to escape and digest a path for sperm to enter into the secondary oocyte
the secondary oocyte responds to sperm penetration by
blocking entry of more than one sperm, which prevents polyspermy from occuring
cortical granules inside membrane of
secondary oocyte are released
secondary oocyte completes
second meiotic division to produce ovum and polar body
the sperm fuses with the ovum to produce
a zygote and the chromosomes unite, which restores the diploid condition
secondary oocyte will degenerate within 24 hours of
ovulation unless it is fertilized
sperm can survive in female reproductive tract for
7 days so fertilization can occur during a one week “window of opportunity” around time of ovulation
if two oocytes are released during ovulation and each gets penetrated by a separate sperm,
two eggs may be fertilized and dizygotic (fraternal) twins result
approx 30 hours after fertilization,
the zygote divides by mitosis and forms two identical daughter cells
mitotic divisions continue to occur every
16 to 20 hours, which produces a collection of blastomeres that form a solid morula
these divisions occur quite rapidly and blastomeres
get progressively smaller, morula remains same size as original zygote
the cells of the morula become
tightly packed through compaction and blastomeres of unequal size begin to form, which creates hollow blastocyst
outer layer of smaller trophoblast cells form
layers around developing embryo
larger cells inside trophoblast make up
inner cell mass
if a single zygote separates completely during cleavage
monozygotic (identical) twins will result
implantation begins
when a blastocyst comes into contact with the endometrium
spontaneous abortions (miscarriages) may occur at this time because
2 out of every 3 blastocysts may not implant due to genetic abnormalities in embyro
as a blastocyst begins to implant,
cells of the trophoblast divide and differentiate and grow into the endometrium to anchor the blastocyst in place and the inner cell mass separates from the trophoblast and differentiates into the primary germ layers of the embryo
ectoderm will form
skin, hair, nails, neural tissue, and linings of mouth and throat
mesoderm will form
bone, cartilage, muscle, and parts of heart, kidneys, and gonads
endoderm will form
most of gut and parts of liver and pancreas, linings of digestive tract and respiratory, and reproductive ducts
four extraembryonic membranes form from the
primary germ layers of the embryo
yolk sac develops from
endoderm and mesoderm to form embryonic blood until liver is established
amnion develops from
ectoderm and mesoderm to surround embryo
amniotic sac fills with
amniotic fluid which cushions and protects developing embryo; also maintains constant temp and pressure
allantois
develops from endoderm near base of yolk sac; contributes to development of urinary bladder
blood vessels in the allantois
become umbilical vein and umbilical arteries
chorion
develops from mesoderm and forms finger-like chorionic villi that penetrate endometrium to establish network of blood vessels
the placenta forms in part from
maternal tissue and in part from embryonic tissue
chorionic villi contain
blood vessels and grow into the endometrium, where they get surrounded by maternal blood sinuses to form the placenta
placenta serves as
a selectively permeable barrier between maternal bloodstream and embryonic bloodstream
blood is never
exchanged and materials “cross the placenta” by simple diffusion
umbilical cord
the amnion fuses with the chorion and they surround the allantoic vessels to form an umbilical cord
umbilical cord attaches belly of
embryo to middle of placenta
umbilical cord contains
two umbilical arteries and one umbilical vein
umbilical vein
carries blood that is rich in oxygen and nutrients from placenta to embryo/fetus
umbilical arteries
carry blood that contains carbon dioxide and wastes from embryo/fetus to placenta to be eliminated
placenta produces
several hormones that are needed to maintain pregnancy
a full term pregnancy lasts for approximately
9 months, or 40 weeks or 266 days and can be divided into two major periods
embryonic stage
typically refers to first 8 weeks of gestation; characterized by development of major organ systems in embryo
fetal stage
typically refers to the last 30-32 weeks of gestation; characterized by organ growth and maturation of fetus
the corpus luteum in the ovary
secretes estrogens and progesterone to maintain the endometrium and prepare the mammary glands for lactation
chorionic villi secrete
human chorionic gonadotropin (hCG) to maintain the corpus luteum, which prevents menstruation that would eliminate the developing embryo
hCG levels in the urine
serve as basis for home pregnancy tests
hCG levels may be cause of
nausea and vomiting associated with morning sickness during first trimester of pregnancy
the placenta eventually secretes
hormones that are needed to maintain the pregnancy
the exact trigger of labor and birth
is not known, but various hormones are involved
steroid hormones
released by fetus from cortex of its adrenal gland
falling progesterone levels
increase sensitivity of uterine smooth muscles to oxytocin (near end of gestation)
oxytocin
released from the posterior lobe of the pituitary gland to stimulate uterine smooth muscle to contract
rising levels of oxytocin
stimulate production of prostaglandins that also contribute to uterine smooth muscle contractions
relaxin
produced by placenta to soften pubic symphysis and dilate cervix
2-3 weeks before labor begins
the fetus drops lower into the pelvic cavity in a process called “lightening” which reduces the pressure on the mother’s abdomen and diaphragm making it easier for her to breathe
during the last week of gestation
the fetus will rotate in the uterus in order to present itself for delivery
the head of fetus
usually moves into the cervix in order to exit first
during the final weeks of gestation
a woman may experience “false labor” characterized by Braxton-Hick’s contractions that are regular and not very strong
true labor is characterized by
contractions that become stronger at regular intervals
Stage I of birth involves
cervical effacement and dilation and lasts from 4-24 hours
cervix during birth
relatively inflexible and must retract upward to expose fetus’s head
cervical canal during birth
has been blocked by a mucus plug during gestation; removal of plug creates bloody discharge into vagina
amniotic sac during birth
ruptures, giving rise to expression “having the water break”
contractions during birth
occur at short intervals and intensity as cervix completely dilates
Stage II of birth involves
the expulsion of the fetus and lasts from 15 minutes to 2 hours
contractions during stage II
reach maximum intensity at 1-2 minutes intervals
head of the fetus during stage Ii
rotates from side-facing to downward facing and extends forward to pass beneath pubic bone
once the head clears the birth canal
shoulders and rest of body slide past pubic bone
crowning
appearance of head of fetus outside the birth canal
episiotomy
may be performed if vaginal canal is too small to permit passage of fetus or if there is danger of perineal tearing
incision of episiotomy
made from vagina to anus; can be repaired with sutures and will heal much faster than uncontrolled perineal tearing
cesarean section
if complications occur during delivery, cesarean section can be performed
breech birth
feet would be delivered first or umbilical cord could become tangled around baby’s neck
size of baby- need for cesarean section
baby might be too large to be delivered vaginally
placenta might detach
prematurely, which could cause uterine hemorrhage
stage II involves
expulsion of the placenta within 15-30 minutes after parturition
uterine contractions during stage III
tear placenta from endometrium to expel “afterbirth”
forceful contractions constrict (during stage III)
uterine blood vessles to reduce hemorrhage
actual milk production is stimulated by
the hormone prolactin (PRL)
high levels of estrogens and progesterone during pregnancy
cause hypothalamus to release prolactin-inhibiting hormone (PIH); blocks secretion of prolactin
without prolactin
mammary glands cannot produce milk
elimination of the plcenta during afterbirth
reduces levels of estrogens and progesterone and allows prolactin to stimulate alveoli in breasts to produce milk
the principal stimulus that maintains milk production
the sucking action of the infant
sensory nerve endings in the nipple
activated by sucking and send signals to hypothalamus so more prolactin is relased’ promotes production and secretion of milk from alveoli into mammary ducts
sucking also triggers
the milk-ejection reflex (milk letdown)
sensory nerves in the nipples send signals to
hypothalamus to release oxytocin
oxytocin stimulates contractions of
myoepithelial cells along lactiferous ducts to pump milk from alveoli through ducts and into nipple
“milk letdown” can become
a conditioned reflex; nursing mother may find that hearing her baby cry or seeing her baby suck its thumb triggers release of milk
the first liquid produced by the mammary glands
colostrum- a yellowish fluid that is high in protein but lower in lactose and fat than milk
colostrum contains
important antibodies and iron-binding proteins
breast feeding maintains
higher levels of oxytocin in a mother’s bloodstream, which causes contractions of uterine smooth muscles that can help restore the uterus to its pre-pregnant state
breast feeding may provide
natural contraception for some women because nursing will reduce GnRH secretion by the hypothalamus, which reduces the amount of FSH and LH released by the pituitary gland
reduction in FSH and LH will
inhibit follicle development and ovulation
